Tested x86_64-pc-linux-gnu, applying to trunk.
-- 8< --
In this PR, initializing the array of std::string to pass to the vector
initializer_list constructor gets very confusing to the optimizers as the
number of elements increases, primarily because of all the std::allocator
temporaries passed to all the string constructors. Instead of creating one
for each string, let's share an allocator between all the strings; we can do
this safely because we know that std::allocator is stateless and that string
doesn't care about the object identity of its allocator parameter.
PR c++/105838
gcc/cp/ChangeLog:
* cp-tree.h (is_std_allocator): Declare.
* constexpr.cc (is_std_allocator): Split out from...
(is_std_allocator_allocate): ...here.
* init.cc (find_temps_r): New.
(find_allocator_temp): New.
(build_vec_init): Use it.
gcc/testsuite/ChangeLog:
* g++.dg/tree-ssa/allocator-opt1.C: New test.
---
gcc/cp/cp-tree.h | 1 +
gcc/cp/constexpr.cc | 27 +++++----
gcc/cp/init.cc | 59 ++++++++++++++++++-
.../g++.dg/tree-ssa/allocator-opt1.C | 12 ++++
4 files changed, 88 insertions(+), 11 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/tree-ssa/allocator-opt1.C
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index addd26ea077..581ac2b1817 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -8472,6 +8472,7 @@ extern bool is_rvalue_constant_expression (tree);
extern bool is_nondependent_constant_expression (tree);
extern bool is_nondependent_static_init_expression (tree);
extern bool is_static_init_expression (tree);
+extern bool is_std_allocator (tree);
extern bool potential_rvalue_constant_expression (tree);
extern bool require_potential_constant_expression (tree);
extern bool require_constant_expression (tree);
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 23a27a962de..e43d92864f5 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -2214,6 +2214,22 @@ is_std_construct_at (const constexpr_call *call)
&& is_std_construct_at (call->fundef->decl));
}
+/* True if CTX is an instance of std::allocator. */
+
+bool
+is_std_allocator (tree ctx)
+{
+ if (ctx == NULL_TREE || !CLASS_TYPE_P (ctx) || !TYPE_MAIN_DECL (ctx))
+ return false;
+
+ tree decl = TYPE_MAIN_DECL (ctx);
+ tree name = DECL_NAME (decl);
+ if (name == NULL_TREE || !id_equal (name, "allocator"))
+ return false;
+
+ return decl_in_std_namespace_p (decl);
+}
+
/* Return true if FNDECL is std::allocator<T>::{,de}allocate. */
static inline bool
@@ -2224,16 +2240,7 @@ is_std_allocator_allocate (tree fndecl)
|| !(id_equal (name, "allocate") || id_equal (name, "deallocate")))
return false;
- tree ctx = DECL_CONTEXT (fndecl);
- if (ctx == NULL_TREE || !CLASS_TYPE_P (ctx) || !TYPE_MAIN_DECL (ctx))
- return false;
-
- tree decl = TYPE_MAIN_DECL (ctx);
- name = DECL_NAME (decl);
- if (name == NULL_TREE || !id_equal (name, "allocator"))
- return false;
-
- return decl_in_std_namespace_p (decl);
+ return is_std_allocator (DECL_CONTEXT (fndecl));
}
/* Overload for the above taking constexpr_call*. */
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index 2fff4ad2dc7..428fac5621c 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -4308,6 +4308,51 @@ finish_length_check (tree atype, tree iterator, tree
obase, unsigned n)
}
}
+/* walk_tree callback to collect temporaries in an expression. */
+
+tree
+find_temps_r (tree *tp, int *walk_subtrees, void *data)
+{
+ vec<tree*> &temps = *static_cast<auto_vec<tree*> *>(data);
+ tree t = *tp;
+ if (TREE_CODE (t) == TARGET_EXPR
+ && !TARGET_EXPR_ELIDING_P (t))
+ temps.safe_push (tp);
+ else if (TYPE_P (t))
+ *walk_subtrees = 0;
+
+ return NULL_TREE;
+}
+
+/* If INIT initializes a standard library class, and involves a temporary
+ std::allocator<T>, return a pointer to the temp.
+
+ Used by build_vec_init when initializing an array of e.g. strings to reuse
+ the same temporary allocator for all of the strings. We can do this because
+ std::allocator has no data and the standard library doesn't care about the
+ address of allocator objects.
+
+ ??? Add an attribute to allow users to assert the same property for other
+ classes, i.e. one object of the type is interchangeable with any other? */
+
+static tree*
+find_allocator_temp (tree init)
+{
+ if (TREE_CODE (init) == EXPR_STMT)
+ init = EXPR_STMT_EXPR (init);
+ if (TREE_CODE (init) == CONVERT_EXPR)
+ init = TREE_OPERAND (init, 0);
+ tree type = TREE_TYPE (init);
+ if (!CLASS_TYPE_P (type) || !decl_in_std_namespace_p (TYPE_NAME (type)))
+ return NULL;
+ auto_vec<tree*> temps;
+ cp_walk_tree_without_duplicates (&init, find_temps_r, &temps);
+ for (tree *p : temps)
+ if (is_std_allocator (TREE_TYPE (*p)))
+ return p;
+ return NULL;
+}
+
/* `build_vec_init' returns tree structure that performs
initialization of a vector of aggregate types.
@@ -4589,6 +4634,8 @@ build_vec_init (tree base, tree maxindex, tree init,
if (try_const)
vec_alloc (const_vec, CONSTRUCTOR_NELTS (init));
+ tree alloc_obj = NULL_TREE;
+
FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (init), idx, field, elt)
{
tree baseref = build1 (INDIRECT_REF, type, base);
@@ -4638,7 +4685,17 @@ build_vec_init (tree base, tree maxindex, tree init,
}
if (one_init)
- finish_expr_stmt (one_init);
+ {
+ /* Only create one std::allocator temporary. */
+ if (tree *this_alloc = find_allocator_temp (one_init))
+ {
+ if (alloc_obj)
+ *this_alloc = alloc_obj;
+ else
+ alloc_obj = TARGET_EXPR_SLOT (*this_alloc);
+ }
+ finish_expr_stmt (one_init);
+ }
one_init = cp_build_unary_op (PREINCREMENT_EXPR, base, false,
complain);
diff --git a/gcc/testsuite/g++.dg/tree-ssa/allocator-opt1.C
b/gcc/testsuite/g++.dg/tree-ssa/allocator-opt1.C
new file mode 100644
index 00000000000..e8394c7ad70
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/allocator-opt1.C
@@ -0,0 +1,12 @@
+// PR c++/105838
+// { dg-additional-options -fdump-tree-gimple }
+
+// Check that there's only one allocator (temporary) variable.
+// Currently the dump doesn't print the allocator template arg in this context.
+// { dg-final { scan-tree-dump-times "struct allocator D" 1 "gimple" } }
+
+#include <string>
+void f (const char *p)
+{
+ std::string lst[] = { p, p, p, p };
+}
base-commit: 3da5ae7a347b7d74765053f4a08eaf7ec58f8735
--
2.31.1
